Windows Management Framework, which includes Windows PowerShell 2.0, WinRM 2.0, and BITS 4.0, has been officially released today.  This down-level release is now supported for Windows XP, Windows Server 2003, Windows Vista, Windows Server 2008, Windows 7, and Windows Server 2008 R2 operating systems.

You can find the release here:  http://go.microsoft.com/fwlink/?LinkID=151321